This invention relates to a control system for a machine or an apparatus, or more particularly, to a sequential control circuit means for controlling the functioning of apparatus such as an electrophotographic copying apparatus comprising various functioning devices including their respective smaller devices to be independently driven through a single driving means via a respective clutch while their respective functioning accomplishments being mutually related from a standpoint of sequential steps, wherein respective sequential instructions for the starting and stopping of the respective devices or mechanical subsystems, including their respective smaller devices are to be specifically controlled through a respective digital timer means constituting the above-mentioned sequential control circuit means, so that all of the devices are successively controlled in a predetermined manner.
According to a conventional sequential control system to be employed for controlling the mechanical machine of the above-described type, respective alternatively timed actuations of operations and stoppings have been accomplished with the help of a conventional digital timer means, which can output a respective pulse defining a specific pulsation interval (alternatively equivalent to the time interval) proportional to the predetermined number of pulses of a pulse train (basic train of clock pulses) at an instance when the number of pulses consecutively generated reaches a predetermined number. More specifically, the conventional sequential control system of the above described type is ordinarily carried out with a digital control system comprising, for example, a microcomputing circuit means provided with the digital timer of the above-described type, in the following sequential order. First of all, the sequential control program containing an operational instruction to call out respective subsystems or devices constituting the machine, including smaller devices as the sequential objects to be controlled in a sequential manner and their respective predetermined operational time data etc., is stored in the memory address of the microcomputer. Then, upon the requirement of the sequential control of the mechanical machine of the above-described type, sequential operational instructions of the respective device and smaller devices and their corresponding operational time intervals are read out through a micro central processing unit CPU, and then, respective operational time intervals (which are commonly each decided from the planning data for the respective devices and smaller devices from a standpoint of the whole sequential control time of the mechanical machine) are successively preset to the specific timer means. Accordingly, the digital timer means which has been preset by the respective data in a manner as described above, are timed with the help of the basic train of clock pulses hving a predetermined cycle, so the the resultant pulse output from the timer serves to control the respective alternative actuation of operation and stoppage of the respective object to be sequentially addressed.
However, according to the timing method of the above-described conventional method, if the operational speed of a certain device varies from the predetermined speed during the operation, the driving of the devices mentioned above is not consistent with that arranged to be actually effected through the present data as mentioned above, and thus results in an inconsistency between the following sequential timings for the actual operation of the mechanical machine and that designed in advance. Therefore, upon the situation as described above, undesirable defects, such as fogging, as far as the electrophotographic copying apparatus is concerned, cannot be avoided.
Conventionally, to overcome the above-mentioned defects resulting from differences between the real and designed operational characteristics with the employment of the conventional control system, some arrangements for maintaining the driving rate, such as maintaining a constant driving speed of the motor, may serve the purpose. However, the unexpected load variations inherently caused by the respective defective production of the devices or the smaller devices mentioned above with reference to the predetermined load level of the respective device or smaller device alternatively causes the fixed electric rating to be varied, and thus, it is difficult to prevent occurrence of variations in the electric source with respect to the fixed electric rating, which consequently results in difficulties in reducing these defects mentioned above.
As for the other measures to overcome the defects described in the foregoing, the successive modification or correction of successive frequencies of the clock pulse train to be sequentially input into the above-mentioned digital timer means in accordance with the respective variations with respect to the respective driving rate in the course of the driving operation of a respective device or smaller device may be considered. However, such successive modification of respective frequencies are not still enough for causing the variations in the driving rate to be effectively compensated, when the magnitude of the inherent defects specific to these devices or smaller devices are to be taken into consideration.
Referring now to FIG. 1, there is shown a conventional pulse generator 8 employing an arrangement of photoelectric coupler 7, operating in synchronism with an operation of the driven means. More specifically, the above-mentioned pulse generator comprises a disc 4, which is coupled to a respective driven shaft 2' of the object mechanical subsystem or device, with the above-mentioned driven shaft 2' itself being connected with a driving shaft 2 of a driving motor 1 through a respective clutch (such as an electromagnetic clutch, however not shown here), and is arranged to have a plurality of slit portions 3 circumferentially regulated by a predetermined central angle with respect to a center of the disc, a radiation lamp 5 disposed to space against the array of slit portions, and a photoelectric element 6 made, for example, of cadmium sulfide, to receive radiation of the radiation light through the array of slit portions mentioned above. According to the above-mentioned pulse generator 8, a train of pulses (here denoted by the second signal composed of the train of pulses), the pulsation of which is proportional to the rate of the respective driven means and is synchronized with the operation of the above-mentioned respective driven means, is generated, so that the timer means mentioned earlier is timed through the second signal. Accordingly, with the help of the arrangement mentioned above, the inconsistency in timing between the sequential instructions to respective driven means and the sequential operations of respective driven means to be conrolled is diminished. However, as long as the arrangement mentioned above is employed for the system control of the mechanical apparatus, since the second signal mentioned above is, in turn, only generated for the driven means equipped with the pulse generator, there is such a disadvantage that the respective controls of the other compulsory smaller devices or instruments to be controlled, such as a temperature controller, paper size controller etc. cannot be performed. To overcome the difficulties for applying the above-mentioned conventional arrangement to the respective instrument, it might be taken into consideration of the situation wherein each instrument is specifically supplemented by the above-mentioned arrangement on the condition that the arrangement is independently kept in an operation mode. However, accomplishment of the above-described situation is rather difficult, due to the secondary problems thereby to be brought about, such as rather high electric consumption, undesirable temperature rise, generation of noise, scattering of the toner particles, etc. Still furthermore, even if the second signal is specially introduced into, for example, the microcomputer means, so that the mechanical apparatus, on the whole, is controlled through the timer means specially provided in the microcomputer, inevitable frequency differences among two kinds of pulses, i.e., about 400 KHz for program processing and about 100 KHz of the second signal, is to affect the capability of C P U for processing the predetermined program, and thus, as is clear from the description in the foregoing, the arrangement is rather difficult to put into practice even in a step of utilization of microcomputer means.